Devices for power transmission between a shaft of an engine and a shaft of wheels used in hybrid vehicles are known. Such devices are described in application FR-A-2832357. These transmission devices comprise generally a thermal engine, and a pair of electric machines. The shaft of the engine, the shaft of the wheels and the shafts of the machines are connected with each other through a mechanical assembly. This mechanical assembly is generally formed by one or several epicycloidal gear trains. The two machines are connected with each other through a connection device comprising in particular an electric bus. These machines behave as an engine or as a generator as a function of the mechanical and electrical energies that they receive on their shaft and on their terminals, respectively.
A power provided by the thermal engine can be, either transmitted directly to the shaft of the wheels through the mechanical assembly, or derived into an electric chain comprising the engines and the connection device. The power derived into the electric chain is transmitted to the shaft of the wheels so as to adjust the torque applied to this shaft, while adapting the torque and the speed of the thermal engine to a point of operation where consumption of this engine is minimal.
In a first configuration of the transmission device, no storage system is connected to the electric bus. In this configuration, the power in the electric chain is quasi null, apart from the losses of the electric machines. The power consumed by one of the machines is then automatically consumed by the other machine. As a consequence, when one machine behaves as an engine, the other machine behaves as a generator.
In a second configuration of the transmission device, a storing system is connected to the electric bus. This storing system can take the form of a battery, a super capacitor, or an inertia machine. A portion of the power derived can then be recuperated and stored in this storing system. The storing battery allows additional degrees of operation of the system. To this effect, the two machines can function simultaneously as engines in an acceleration mode. In addition, in a specific energy recuperation mode, the two machines can function simultaneously as generators, so as to store a high amount of energy.